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can aircraft cruise speed be less than corner speed? my r-c PROPELLER plane calculations are saying cruise speed is less than corner speed.(Long read)
I have designed an aircraft and wanted to determine its performance charachteristics.
the following parameters have been utilised:
aircraft specifications:
Mtow = 1.7kg
wing_area = 0.411 m^2
Cl_max = 0.7787
Neg_Cl_max (dive against wind@-8deg) = -0.2792
Cd vs cl relationship: Cd = 0.01905227+ 0.123215108*Cl^2
max_pos_load_factor = 2.5
max_neg_load_factor = -1.25
cl vs AOA = Cl = 0.0766*AOA(deg)+0.3317

atmospheric data used:
density = 1.162 kg/m^3
using the following data i tried to draw a V-n diagram which is as follows:

for the calculations I have utilised the following formulaes:
Vstall = sqrt(2W9.81/(rhoSCl_max)) = 9.47 m/s
V_corner speed = Vstall * sqrt(load_factor_max) = 14.97m/s = approx 15m/s
dive speed or max_speed = sqrt(2* load_factor_max * W *9.81 / (rho * S *Cl_0deg)) = 22.78m/s
for the cruising speed I have used the following condition of max (Cl/Cd) for max range.
Cl_(Cl/cd_max) =sqrt(Cdo/K) = 0.3932
corresponding Cd = 2*Cdo = 0.0381
which yields a cruising speed of
V_cruise = sqrt(2w9.81/(rhoSCl_(cl/cd_max)) = 13.32m/s !! which is less than the corner speed graphically calculated.
my question is how exatly is cruising speed of an airplane calculated. I have used the max Cl/cd condition to get max range.Are my calculations wrong somewhere?
Can i use the following method to determine cruise_Speed
using the current V-n diagram i know my cruise speed must be greater than 15m/s.
I have the following formulaes for cases:

Cl/cd max which gives me
Cl = 0.3932 @ 0.08 deg(using Cl vs AOA graph),Cd = 0.0381

2)minimum power condition
cl = 0.6811 @ 4.566 deg, Cd = 0.0762

3)0 deg cruising flight
cl =0.3317,cd = 0.019
Now knowing the aero_values at respective orientation i plot graph between drag and velocity of plane with thrust vs velocity of cruising plane and seek the intersection at various throttle settings of motor as shown.

Here are my questions:
Am i wrong somewhere in my calculations? (i tried many times could use an external eye)
I know experimental data is ultimately used but why are hand calculations so off?
how is actual performance determined in industry
How does the v-n diagram of a fighter-jet/ acrobatic aircraft vary that to a commerical passenge/transport aircraft.
thank you for your valuable time.I hope you have a good day

Welcome to Aviation SE, Raptor.  Can you simplify this to only one question?  That format works best for a Q&A site like this.

out of curiosity why are pos and neg load factor bounded to so small values? (Mtow, wing area and square cube law should allow an airframe easily withstanding 10 times those loads)

hi there the entire wing and tail is held by a 3-d printed coupler that is a few layers thick.

Nobody here is going to check your homework.  Providing so much detail is not useful here.  Likewise, posting excerpts from your professor's notes (perhaps these are your versions of the notes) is questionable.
Your most likely error is one of units.
In any case, corner speed has no relation to cruise speed.  Corner speed is linked to the choice of load factor -- you could choose a very low or very high load factor.  One way or the other, it is going to change how it relates to cruise speed.  What if your maximum positive load factor was 1.1?  What if it was 100?


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Why doesn't KJFK use stop bar lights?
I was wondering why a large airport like KJFK doesn't use stop bars for their taxiways? Specifically I was looking at taxiway KD and from google maps and from videos online it looks like they only have runway guard lights and no stop bar lights? Is there a reason behind this? or is it simply because of costs? or maybe they do have them and I'm just blind (which could be the case).
What is more confusing is that an airport like CYYZ has stop bar lights for runway 06L but no bar lights for RWY 23 taxiway H yet for some reason has them on the other side of RWY 23 on taxiway J.
Thanks in advanced, any information is helpful.
EDIT: It looks like from what I can gather, that stop bar lights are really only used for low visibility. CYYZ has a low visibility procedure chart which outlines that 06L and 05 runways are to be used in these situations. When looking around I can clearly see stop bar lights on the entrances to these runways.
Runway 06R however is not on the low visibility procedure and from images i can find does not have stop bar lights.
I asked an airline pilot, and they claimed that since KJFK is a rather old airport and in an area that generally doesn't have much low vis situations that they just decided not to install them yet. They also stated that most newer airports will install these stop bar lights regardless of where they are.
Diving in deeper it seems that KJFK has tested out stop bar lights in the past but did not install them. probably for the same reason randomhead claimed about it being the costs involved in installing the system.
As for my question with CYYZ 23 taxiway H not having stop bar lights, it does, just further back at the CAT 3 hold.
Let me know if I'm still missing something or if something I said is wrong.

Knowing absolutely nothing about JFK or how their operation works, I can confidently tell you that the answer is "money." Specifically a lack thereof.

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How would I have determined that the airspace overlying and within 5 miles of Barnes County Airport is Class G?
(Refer to Figure 26, area 5.) The airspace overlying and within 5 miles of Barnes County Airport is
A. Class D airspace from the surface to the floor of the overlying Class E airspace.
❌B.Class E airspace from the surface to 1,200 feet MSL.
C.Class G airspace from the surface to 700 feet AGL. (this is correct)
"The Barnes County Airport is depicted inside the magenta shading, which is controlled airspace from 700 feet AGL up to but not including 18,000 feet. Therefore, the airspace below 700 feet AGL is Class G."
Studying for my private pilot exam, airspaces on the charts are a little confusing for me right now. The Magenta shading on the legend of sectional charts is specifically what is confusing me here. Why is the answer option C instead of option B? The two magenta shaded lines on the sectional charts legends both indicate class E, but one refers to Class G and the other does not. The explanations underneath them don't really make sense to me.
Thank you in advance to all the friendly folks who help me answer this.

I did some googling. As an fun aside for colour, the reason this airspace is restricted is because they fly Predator drones in it, and the laser systems on them are not eye safe, meaning they pose a special hazard to other pilots. https://www.federalregister.gov/documents/2012/06/20/2012-15008/establishment-of-restricted-areas-r-5402-r-5403a-r-5403b-r-5403c-r-5403d-r-5403e-and-r-5403f-devils

Practically speaking, Class E airspace can extend upward from any of the following three options:

0ft AGL. This is depicted by a dashed magenta line.
700ft AGL. This is depicted by a shaded magenta line.
1200ft AGL. This is depicted by... nothing. This is the default state of Class E airspace and so it is not specifically charted. (See note below.)

BAC is surrounded by a faded magenta line. This is the second possibility: Class E begins at 700' AGL. Therefore the airspace immediately above the surface (in fact, from the surface up to 699' AGL) must be Class G.
You know that Answer B is not correct because it says that the Class E extends up to 1200' AGL. This is not what Class E does. Wherever it starts, it extends upward from that point until it reaches a higher class of airspace, like a Bravo shelf. If there is no otherwise-charted airspace above it, it extends up to the beginning of Class A airspace at 18000' MSL. Also, Answer B says the Class E begins at the surface. That would be depicted by a dashed magenta line, as at JMS, not a faded magenta line.

The two magenta shaded lines on the sectional charts legends both indicate class E, but one refers to Class G and the other does not.

A simple faded magenta line depicts Class G from the surface to 700' AGL within the line, and Class G from the surface to 1200' AGL on the outside. If there is text "CLASS G" on the hard side of the magenta line, that means that the airspace on the hard side is Class G all the way up to 14500' MSL. See the note below, and see my answer to this question for an example. This is a very rare configuration.
In both cases, Class E airspace lies above the Class G airspace.

A note. Very technically the actual "default" for Class E is that it only extends upward from 14500' MSL. However there are so so so many areas where it is defined as going down to 1200' AGL that the real default is that 1200. They used to chart a blue shaded line around the entirety of the USA border to signify that fact, but these days they just say on the sectional "The default is 1200' and up." There are only one or two areas of true uncontrolled-up-to-14.5 airspace left in the contiguous US.

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Question on a flapped vs non-flapped wings local lift coefficients
I'm developing a workflow in XFLR-5 for adding flaps/control surfaces to a wing design, and I encountered an interesting thing in my data results that I wanted some more insight on. In plotting a local lift coefficient graph, I noticed expectedly that the lift coefficient increased where the flaps are and had downward spikes at the ends of each flap, but interestingly all the non-flapped areas are still slightly higher overall.
In the picture, red is the ordinary wing, and blue is the same wing with a 10 degree flap hinged at 80% of chord length:
It increases at the flapped area and shoots down at the ends of each flap like you'd expect, but why is the blue graph overall higher than the red despite the non-flapped area being the same angle of attack, airspeed, and airfoil shape? Is this an error in my simulations or is there a phenomenon/reason for this difference? If so, what is it?

The bound vorticity in the wing is substantially increased by the flap.  This is predominately felt in front of the flap, but it extends everywhere.
The bound vorticity is directly related to the circulation of the sections.  It causes downwash at the trailing edge and upwash at the leading edge.
The upwash on the outboard parts of the wing causes an effective increase in angle of attack and pushes them to higher lift coefficient.


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Book for non-aviator to undersand flight
I'm not a flyer (and likely never will be), but I'm fascinated by flight.  If I'm not trying to actually become a pilot (so I'm not concerned with all the minutia of safety regulations, certification, airline practice, maintenance, etc.), but just want to understand the basic dynamics of flying a plane (so that if I'm in a plane falling out of the sky I at least understand why), what should / could I read?
EDIT: Most lists I have found online follow the format of "Best Aviation Books" or "Best Aviation Books for new Flyers".  Which doesn't really apply here. Thx

Your question might be closed, as this is opinion-based. I think Flying: Answers From Inside the Cockpit has been popular, it's from a pilot, written for passengers, so it's accurate without the painful theory. Another suggestion is to look at flight simulation games user guides, they are accurate. Instructor Rod Machado (not the surfer) has many interesting videos online.

How technical can it be?

@mins thanks will check, sophit I'd prefer non technical as I feel a general overview shouldn't be bogged down in dense theory, but I'm also not afraid of 'technical' by any means

Wing push air down = air push wing up. Don't forget this on your journey, as many people will make it seem more complicated than this. Good luck!

If the topic is general interest, just going for a wander here in the 'related questions', finding someone who writes answers that suit you and exploring their other answers can be an entry point. See also some of the question tags such as https://aviation.stackexchange.com/questions/tagged/airline-operations or the classic https://aviation.stackexchange.com/a/2223/60886

I'd recommend ANA -- Aerodynamics for Naval Aviators by HH Hunt Jr.  It is a bit technical, but without a lot of heavy derivations.  You can find inexpensive paperback copies online or download a PDF from the FAA https://www.faa.gov/sites/faa.gov/files/regulations_policies/handbooks_manuals/aviation/00-80T-80.pdf

The FAA publish the Pilot's Handbook of Aeronautical Knowledge which is available as PDFs here: https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak  It's pretty comprehensive.

Aerodynamics for Naval Aviators  Is a classic used for pilot training.  It covers some aerodynamics as well as aircraft performance (how airplanes fly).
It is a little technical -- but without getting bogged down in all the derivations.  In my opinion, it is not possible to really understand this stuff without at least a few equations.  ANA skirts that minimum.
It is a publication of the US Government (NAVAIR) and is printed and made available by the FAA.  You can get an inexpensive paperback copy at any pilot shop or online.

This sounds like the type of book I'm looking for. I also find military manuals often stick to "just what your really need to know".  I'll throw it on my ereader and give it a try.


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Can you receive traffic advisories without a specific destination or intention?
I’m wondering if it is possible to call up the local approach facility and ask them for flight following even if you are just doing sightseeing or something. Do you need to tell them your intended route, altitude, and destination? How would you ask them for flight following without a specific destination?

Are you asking about a specific country? Procedures may be different in different parts of the world.

In order for a TRACON or tower to enter you in for long-distance flight following (which in my lexicon is the only type of "flight following," though the official documentation doesn't differentiate) we need to create what is essentially a limited-information IFR flight plan for you. The minimum required information to enter this plan is your callsign, destination, and type. A cruising altitude is not strictly necessary but leaving it out can mess up the transfer of the tag down the line, so you should always give it.
If you are not going to be handed off from facility to facility, but will be remaining within the airspace controlled by one single facility, we can enter you in for an isolated "local" code that does not interface with the flight data computer at the center. Route of flight, altitude and aircraft type are still good things for the controller to know, but the minimum information necessary to enter you into the system is nothing more than a callsign.
A Center controller might not have the option of entering you in for a "local" code so they might need a rough destination no matter what. I'm not experienced with the Center systems.
You should say something along the lines of "request traffic advisories in the north practice area" or "traffic advisories for a skyline tour" or "transit the Charlie at 3500" or "aerial survey at 4700" or whatever it is you're looking to do.

The excerpt above, from the FAA Air Traffic Control Handbook, describes a Terminal function, which doesn't apply to Centers. Our rules for VFR services, however, are similar.
A Center controller would have the option of providing services on a workload basis. Keep in mind that there are factors besides workload, such as frequency and radar coverage issues. We get frequent requests from photo missions that fly grid patterns (which we may not have access to, for whatever reason), round robin, cross country, aircraft checking on cattle herds and oil pipelines, and yes, sightseers. We will need your planned route of flight to be able to provide the best services, even if it's something like "We plan to fly up to Devil's Tower, then over to Rushmore, then back to Chadron". (A very nice scenic flight, BTW)
Our VFR services include traffic, terrain, and airspace advisories, as well as displayed weather along your planned route. We also have access to AIRMET information for the sector.
In my opinion, calling up an ATC facility for flight following is cheap insurance.

Are you able to get a squawk for someone without entering a destination? In the terminal world we can enter a full FP plan on the FDIO, or in STARS enter callsign/dest/type/alt (I think you guys can do this with the VP command?), or also in STARS simply enter a callsign (and optional type) and it will generate a local code.

In an ARTCC, we can request a beacon for an aircraft, and track it without flight plan information. Usually, I would ask for some information, such as aircraft type, qualifier, destination, and planned route for a VP.
This allows automation to do things like forward data to the next controller, and is useful in search and rescue, should it be necessary.

In the Center, we can use a local code, or, just leave you on the VFR squawk, if you're staying in a particular sector.
In ZDV, sectors are pretty large, and that Chadron..Devils Tower..Mt. Rushmore..Chadron round robin is in one sector, a sector which is roughly 180 NM wide, and 230 NM tall. I could flight follow you from Scottsbluff, NE to Lusk WY, then to Newcastle, WY, to Philip, SD (with a 70 mile transition to Ellsworth AFB control), to Valentine, NE, to Ainsworth, NE, and back to Scottsbluff. That's nearly 700 nautical miles, and well within the sector boundaries the entire time.
Would I use a handwritten flight strip and not ask about your aircraft, if I knew you were going to round robin in my sector for 5 hours in a Skyhawk? No way.
You'd get a standard squawk, and I'd ask you for your aircraft type, qualifier, and planned route, and probably some particulars as you neared airports in your VFR plan. (planning touch-and-gos?, fuel stops?, diverting a few miles to buzz a neighbor ?(don't tell US about THAT!))
Everything else aside, CALL US! You've paid for the service in fuel taxes, licensing, certification, and a myriad of other levies that I have no idea about.
The worst that can happen is the controller is too busy. In the US, if the service CAN be provided (based on workload, radar, etc.), it SHALL be provided.
Call us.


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Why is there a "-D" circling-only approach at an airport that does not have corresponding -A, -B, and -C approaches?
There are three instrument approaches at SEE (as of 17 June 2021):

RNAV (GPS) RWY 09L
RNAV (GPS) RWY 17
LOC-D

The two RNAV approaches are straight-in to runways 09L and 17, respectively. The LOC-D approach is aligned with runway 27R but has no straight-in minima. The -D in the approach name indicates that fact.1
The fact that the suffix is -D implies the existence of LOC-A, LOC-B, and LOC-C approaches at SEE. These approaches do not exist. Why, then, is the LOC-D approach named that way? Did the other approaches exist at one point and have since been removed?
In general, is there any way to look up the historical instrument approaches at any given airport?

1 7110.65 4–8–1a Note 6: "Alphabetical suffixes with a letter from the beginning of the alphabet; for example, A, B, C, denote a procedure that does not meet the criteria for straight-in landing minimums authorization" and AIM 5–4–5a3(a) "Circling only approaches are identified by the navigational system providing final approach guidance and a letter (e.g., VOR A)."

"The fact that the suffix is -D implies the existence of LOC-A, LOC-B, and LOC-C approaches at SEE." Actually there is a subtelty: According to Order 8260.19 (or FSIMS 404.g.2), for terminal procedures:

The alphabetical suffix for circling procedures must
not be duplicated at airports with identical city names
within one state.
Regardless of the airport name, successive suffixes must
be used for all airports that serve the same city.

In accordance, the suffix must be unique for San Diego city, not for Gillespie Field airport.

Other civil airfields serving San Diego per FAA registration include: Lindbergh Field (KSAN), Brown Field Municipal Airport (KSDM) and Montgomery Field (KMYF). More.
It is possible -A,-B,-C are not used anymore (I've not checked), but -D will be kept for this procedure as long as it exists.
The same question was asked and answered on this blog. The original author, Russ Roslewski, is the one to receive the credit.


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Why shouldn't variable pitch propellers be operated at low speed?
Aircraft with variable pitch propellers usually have a red arc on the propeller speed gauge somewhere between about 500 and 1000 rpm, often accompanied by placard like "stabilized propeller operation between 500 rpm and 1000 rpm is prohibited" (the range is slightly different in different aircraft).
What is the reason for this restriction?

The specific reasons may be specific to each propeller/engine combination, but in general it seems to be related to stresses.
According to this King Air POH on page 2-2:

Stabilized ground operation between 400 and 1,150 propeller RPM is prohibited. Operation between 0 and 400 propeller RPM is permissible only with propeller feathered.
STABILIZED GROUND OPERATION WITHIN THE PROPELLER RESTRICTED RPM RANGE CAN GENERATE HIGH PROPELLER STRESSES AND RESULT IN PROPELLER FAILURE AND LOSS OF CONTROL OF THE AIRCRAFT.

This is probably due to the frequency of the aerodynamic forces at those RPM's resonating with the frequency of the propeller, and getting amplified to unsafe stress levels. This is called ground resonance and is also an issue with helicopters. In addition to over-stressing the propeller blades, it can also affect the fatigue life.
There is also a discussion in this thread, and it is mentioned in this guide.
As voretaq7 mentions, fixed-pitch propellers have similar restrictions for similar reasons. Some engines include a damper that removes this restriction by damping out the resonance.

It's worth noting that fixed-pitch propellers attached to certain engines can have similar restrictions (e.g. "Avoid continuous operation between 2150 and 2350 r.p.m.") - these restrictions are usually imposed for similar reasons (resonant vibrations causing excess stress, possibly leading to early propeller failure).

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Why do aircraft piston engines require priming?
Aircraft piston engines generally require priming, but automobile engines don't seem to need it. Why doesn't cranking the engine with the starter pull in fuel mixture that would ignite without help of the priming?

All carb engines needs priming after it's been sitting for a while and the carb has dried up. Right now very few cars uses carbs and even when carbs were popular on cars, most cars never sit so long to have a dry carb. However, it's not entirely correct that fuel injected cars doesn't need priming,  it primes every time after you turn on the electrics (the light noise you hear when the speedometer sweeps).

Remember the choke in older cars? Of course do car engines start better with priming, but automatic control has taken that off your hands and made it invisible. Another sign that aircraft piston engine technology has stood still in time.

@PeterKämpf The choke is more like the mixture than priming, though. The choke just richens the mixture to make it easier to start when cold. Agree with the sentiment though

@Peter Kämpf: Yes, and in the days between actual hand chokes and EFI, you'd pump the gas pedal a few times to squirt some extra fuel into the engine (via the accelerator pump).  And on really cold days you might have to prime it with a few squirts of starting fluid.

@user3528438: I don't know what you mean by "when the speedometer sweeps".  Maybe that's something specific to your particular car?  But I strongly suspect that the noise you're hearing isn't the engine being primed, it's the electric fuel pump building pressure in the system.  "Priming" would be controlled by the EFI system, and wouldn't happen until the engine cranks.

Modern car engines are really very sophisticated compared to most airplane piston engines, which are 70 year old technology.
Modern cars typically have an electric fuel pump in the tank which is often started by opening the drivers side door, by the time your butt is in the seat the fuel system is pressurized. When the ignition system is activated the ECU (engine computer) looks at engine coolant temperature and outside air temperature and directs the electronic fuel injectors to meter the exact amount of fuel which is correct for the conditions, directly into the inlet valves. A cold engine needs a much higher ratio of fuel to air when starting (2-3 times when hot), which reduces as it heats. When it starts running the ECU also takes into account the mass of the air flow and oxygen content of the exhaust to maintain the ideal fuel-air balance for the smooth and efficient running of the engine.
This technology does exist for airplane engines, it's just expensive to fit so very few airplanes have it. Most light airplanes have very simple, completely manual systems. You shut down the engine by cutting off the fuel supply (closing the mixture), this ensures that the engine is completely dry of fuel so that if the prop is spun there's nothing in the cylinders which could go foom and spin the prop, potentially maiming someone.
Piston engines create a lot of suction as they operate, and rely heavily on vacuum suction to operate. The low pressure in the carburetor atomizes fuel, which then gets pulled into the cylinder, explodes which in turn pulls more fuel and air in. However, because the mixture was cut off the engine and carb are all dry (any fuel left in the carb bowl will evaporate over time), which produces little suction. No suction, no atomization of fuel, no foom. The primer pumps a very rich atomized mist of fuel into the intake for each cylinder, giving the engine something to foom, creating suction to pull fuel through the carb and sustain the engine. This is why you feel resistance when using the primer, you are forcing it through a bunch of atomizing nozzles. This is why you need to start right after priming, if you wait too long you lose atomization.
Note that many airplane piston engine carbs have accelerator pumps which jet raw fuel into the carb on quick throttle advances, this is to prevent a lean cut-off. Some people think it's the same as using the primer, but it isn't at all. Because there's no suction when you pump the throttle forward all you are doing is jetting liquid fuel into the carb, there's no vacuum to atomize it, so all you are doing is filling cylinders with raw fuel and they won't go bang. A single jet is good because having fuel in the carb bowl gives something to atomize once it catches, but too much will just flood the engine.
A hot start is very different from a cold start, the engine doesn't need as rich a mixture and the carb bowl still has fuel in it, so when you crank it you don't need to prime in most cases.

I always think of F words when I think how old the technology in my airplane engine is @DeanF.

I also understand pumping the throttle instead of priming can cause fires.

Downvoted because the carb is not dry after idle cut off or when starting the engine. Also downvoted because the answer makes no mention of cold engines requiring an enriched air fuel mixture when starting.

Fuel does not explode in an engine, it burns.

Given all the downsides of carbs I'm surprised the safety culture of aviation still allows them.

@Adam: A fuel-injected engine generally needs a lot of electronic components to be working correctly in order to be functional.  The only "electronics" needed to make a carbureted engine work are a tapped coil of wire, some contacts, interconnecting wires, and spark plugs.  Those things are cheap enough that it's practical for a plane to include two completely independent ignition systems, and simple enough that it's unlikely both would fail at once.

@supercat AFAIK no one crashed due to FI icing. Electronic components are both reliable and cheap enough for redundancy. They also don't wear out, seize, clog, or jam like mechanical components can.

The carb bowl will typically be dry in a typical cold-start @MikeSowsun, I've edited to make that clear. I have also emphasized the need for a rich mixture.

Thank goodness they're 70 year old technology. I would not trust anything else.

Nowhere do I say the technology doesn't exist for airplane engines @BigNutz, I say it does exist but is expensive to fit.

@GdD You are absolutely right, I must have misread what you wrote. Add to that the normal lack of awes

No problemo @BigNutz.

@GdD awareness by the GA community that these are a thing (Continental's fault), I saw what I expected, and it was wrong. Sorry about that. You're spot on about them being expensive too. Is there a way to edit these comments?

You can edit them for about 2 minutes after you write them by clicking on the edit link, after that they are frozen @BigNutz. I usually cut and paste into a new comment, make the changes, then delete the original.

Just a quick comment regarding the quite accurate statement that "this technology does exist for airplane engines, it's expensive to fit". This is 100% true. The engine is a 4 cylinder, horizontally opposed Continental Motors TCM IOF-240 model. Some of you might remember a rare newcomer to the single engine crowd, Liberty Aerospace HQ'd in Melbourne, FL. Liberty, along with Continental, successfully achieved full 14CFR Part 23 Type Certification of the aircraft.

As a former Reg. Sales Manager with upwards of 700 hours flying them, even after certification, the FADEC system was buggy and needed refinement. But it does work, no mixture control, the FADEC controlled the fuel mixture and ignition spark intensity and duration for each of the 4 cylinders separate from the others. The company didn't get through the 2008 collapse, but I'm certain the engines are still being offered for those looking to retrofit. I hope that after 12 years the kinks have been worked out.

Aircraft piston engines require fuel priming or fuel enrichment only when cold. This is true for ALL piston engines.
Fuel enrichment is needed because the cold temperature does not allow the fuel to properly atomize/vaporize in the air-fuel mixture and may actually condense back into raw fuel on the cold interior surfaces of the engine. Fuel enrichment ensures that will be a proper air fuel moisture reaching the cylinders for starting.
In a carbureted automotive engine, fuel enrichment is done with a manual or automatic choke.
Typical carbureted aircraft piston engines do not use a choke but instead use priming lines to supply addition fuel enrichment.
On a four cylinder aircraft engine there can be one, two, three, or four priming lines which spray atomized fuel directly into the engine cylinder very close to the intake valve. These priming lines are typically 1/8” copper tubing. It is easy to over prime the engine, and some pilots prefer not having a primer line for each cylinder. Having fewer priming lines allows one or two cylinders to fire even when the others are over primed.
Here is a photo showing 1/8” copper priming lines connected to the engine near the intake valves.

Hm, I remember that 30 years ago the car did indeed have an enrichment lever that you'd pull if it wasn't starting and try with that (and then it was sluggish if you forgot it on, because the mixture was too rich).

Yes, in the UK, i believe it was called a "choke"

Why we need enrichment in the first place?
The gasoline is liquid. The ignition requires a mixture of air and gasoline vapour.
In a running engine, having enough air inlet speed, gasoline becomes mist that evaporates when the compression happens in the cylinder. The engine being hot also helps a lot.
When cranking a cold engine, the air speed is not enough to create a mist, you get larger droplets that are quick to reach the inlet and combustion chamber walls and settle there. The compression is weaker, so is the heating because of the compression. No enough gasoline vapour - no ignition. The solution? Add more gasoline to the wannabe mixture that refuses to mix.
Carburetted car engines (~30 years ago) had the choke valve that reduced the pressure in the carburettor, alowing more gasoline to be drawn into the air stream. The choke valve is a bit of reliability concern - it has to be able to almost completely close the air inlet, or it won't work. I think that's why it is generally not used in motorcycles and probably in aircraft as well. A choke valve not returning completely was a common failure mode and one won't notice until the full power is needed.
One still needs some enrichment in order to start the engine. In the aircraft, one wants a method that has rather low probability of killing the engine in mid-air. So we have priming.
And yes, car engines get priming, too. In modern injection-fed computer-controlled engines, an automatic single injection pulse before starting does the trick. Depending on the conditions, the ECU may use priming, starting enrichment (longer injection times when cranking), both, or nothing.
And I am sure I did (as well as almost any advanced driver) manual priming (remove the air filter and pour some gas directly into the air inlet of the carb) on many cars that refused to start in a cold weather a decade or two ago.

"one won't notice until the full power is needed.".  Which is exactly what you need at takeoff, and you'd be very likely to notice before you reach V1 (if indeed you even can at severely reduced engine power).  On aircraft this is probably less of a safety concern than in other applications.

A piston engine is a constant-volume pump, so the compression clearly does not depend on rotation speed (for normally aspirated engine; it does for the turbocharger).

@JanHudec An ideal piston engine is a constant-volume pump. Real pistons and valves have leaks and these leaks become significant at low rpm and also tend to increase with hours/mileage. That's an important (but not the only) reason why older engines are harder to start.


text:
How many crew does a P-8 operate with?
According to Reuters, Iran says it refrained from shooting down U.S. plane with 35 on board. The article goes onto say the aircraft was a P-8 Poseidon with 35 on board:

Iran refrained from shooting down a U.S. plane with 35 people on board
  that was accompanying the downed drone in the Gulf, a Revolutionary
  Guards commander said on Friday...
Amirali Hajizadeh, head of the Revolutionary Guards aerospace
  division, was quoted as saying by Tasnim news agency: “With the U.S.
  drone in the region there was also an American P-8 plane with 35
  people on board. This plane also entered our airspace and we could
  have shot it down, but we did not.”

I thought the P-8 had a crew of about 12 or so. I thought two or three were flight crew, and the remainder were technicians working with the electronic warfare packages.
Is 35 an accurate number for the P-8?

The P-8 is larger than a 737 so 35 people isn't unimaginable, but all the sources I can find says that it has a mission crew of 7.

The P-8 is literally a 737.

Yes, its late.. I meant it was longer than the 737 "C-40" transport plane.

OK, according to wikipedia: "Crew: Flight: two; Mission: seven". I missed it on my first reading. I wonder why Iran is reporting 35?

They were thinking RC-135.

This diagram clearly shows it would be almost impossible to fit nine crew plus an additional twenty-six people in the aircraft. There are no seats for the additional twenty-six. At most you can fit two additional people in the observer seats behind the power distribution packs. The additional seats in the middle are for crew only during takeoff and landing. The aft cabin only has one seat for the mission planning workstation, and that's one of the nine crew seats.

Nitpicking, but it looks like the forward cabin seating is drawn as three rows of dual seats, not single seats...

That's actually where the crew sits for t/o and landing. Not pax seats.

Ah ok, makes sense. Is that the same (crew in seats and not at station for takeoff/landing) on other similar aircraft, e.g. Orion or Nimrod?

I am not familiar with the config for those.

Understood, thanks!


text:
When an airliner gets lost, and receives warning shots from interceptors, how should the pilots react in order to save the aircraft?
In 1983 KAL007 was shot down by the Soviets, as it got lost due to navigational errors and entered restricted airspace. The Soviet interceptors reportedly fired warning shots "which were likely not seen by the KAL pilots", and after then they proceeded to destroy the airliner with an air to air missile.
So, let's suppose you are flying a commercial flight, when a military aircraft catches up to you. If your communication equipment wasn't malfunctioning, you would have already gotten demands to change course and you could have identified yourself, answered that you will comply, and could more easily avert the problem. For this case, let's suppose your comms are down due to technical problems.
You then see you are fired upon (how? smoke trails of a missile flying by? Tracers from guns whizzing past?). It is only then when you realize you got intercepted, and you suddenly realize they just fired warning shots at you.
What now? How could you maximize your chances of survival? I would guess you have to indicate surrender, that you will comply to any instructions, and that you mean no ill will. How can you do that without a working radio? If you just entered a country's territory, the most obvious way would be to change course to the shortest path leading out of that territory, but if you are deep inside, or you are lost, you might choose the wrong heading and make the problem even worse.
Is there a custom how a civilian aircraft can indicate "I yield, please don't shoot me, I will follow your orders!"? And, lastly, how would it differ between the incident happening in 1983 versus 2019?

This question will probably not be well received as it is obviously an invitation to a discussion.  Lowering landing gear would be a signal of being willing to land.

@quietflyer : I don't want to invite any discussion about what happened with the KAL007, neither do I want a discussion about why would countries shoot at private aircraft, or about any other topic. The question is about any well-established customs which apply in such a situation. Or maybe there are instructions during training for pilots what to do? Or any established or recognized protocol, even if not written, then at least de-facto recognizable. If you think lowering the landing gears is one, you are welcomed to post it as an answer. (would it even work without damage at mach 0.8?)

Related, but probably not quite a duplicate: https://aviation.stackexchange.com/questions/9412/how-do-fighter-jets-communicate-with-an-intercepted-plane-thats-lost-comms

This question was asked after yours, but it might answer it

First off there are established interception procedures under international law so they are not going to shoot at you upon overtaking you.  Typically an element of fighters form up on the jet with the leader maneuvering into formation on the jets 9 O’Clock and the Wingman stays on the jet’s six.  They will do so in a manner which allows the intercepted aircraft to see the lead fighter.  There are a series of established visual signals ie rocking wings for compliance, deploying flaps and landing gear, etc.  if the intercepted aircraft cannot communicate with the fighters or ATC, they will squak 7600 and ATC can relay this to the fighters.  Other means can be employed to get the attention of the intercepted aircraft such as the lead fighter cutting in front of the intercepted aircraft while in afterburner, etc.
If it does come down to where the authorities determine you are a threat and use of deadly force becomes authorized, the fighters are going to let you know in a clear and unmistakable way.  Unless you are armed and intend to engage, you better comply!

Have the interception procedures been introduced since the KAL007 incident, or were they in place (and presumably ignored) at the time?


text:
How can best glide speed be lower than best rate of climb speed?
I was looking up V-speeds for C172. I don't have easy access to an official copy of the POH, but online I found:

$V_y$, best rate of climb speed (at sea level): 76 KIAS (p22)
$V_{glide}$, maximum glide speed: 65 kts (p15).

But I always thought that $V_y$ is the speed for highest L/D, which should give both highest rate of climb and lowest rate of descent, and that longest glide is achieved by flying slightly faster than that, because drag grows with square of speed, and therefore it initially grows slower than speed above the minimum drag point.
So why is the $V_{glide}$ quoted lower than $V_y$?

This question contains a misconception.  The glide angle can be expressed as a simple trigonometric function of the L/D ratio, and as a result,the  flattest glide in still air DOES in fact occur at the airspeed that yields the greatest L/D ratio.   The airspeed for minimum sink rate will always be lower than this.  This observation doesn't actually answer why Vy is apparently higher than Vglide in the specific case explored in the question, but it does point out something that could be improved in the question (if it's not too late to do so without invalidating an existing answer.)

@quietflyer, indeed, vertical speed times gravity constant is power, but drag is force. Angle times gravity is force, which would suggest best L/D should match best angle. That does not seem to match the common wisdom though.

@quietflyer, well, I've acquired the idea that max L/D (sans the propeller effects; those complicate the matter a lot) is where best rate of both climb and descent is somewhere along the way, but I don't remember exact reference (it had to be on this site though).

… it might have been me misinterpreting the power curve somewhere though.

Maybe my new answer will help.  Forgetting about propeller effects, we would say that max glide angle occurs at max L/D airspeed which is essentially the airspeed where Drag is minimized.  The minimum sink rate airspeed is always slower than this point.  The minimum sink rate airspeed is (forgetting about propeller effects) the airspeed where the least power is required to maintain level flight.  If the power available from the propulsion system were independent of airspeed, the minimum sink rate airspeed would also yield the max rate of climb.

So your question about why max climb occurs faster than best glide is a good one.  There is just a small error in your suggestion about the meaning of the speed for max L/D.  That is the airspeed that yields the best glide ratio (flattest glide), not the airspeed that yields the lowest sink rate.   See my new answer for more--

The best glide speed is the speed where tangent line from the origin (zero horizontal and vertical speed) touches power curve (for unpowered airplane).
Best rate of the climb is the highest point of the power curve.
When we start with unpowered airplane, the direct equivalent of best rate of climb is lowest rate of sink. The speed for lowest sink will be clearly lower than the best glide speed.
If we would assume that aircraft engine is a magical device, which simply adds some fixed amount of mechanical energy to the airplane regardless of what, then the "powered" power curve would be simply the "unpowered" one shifted up in the graph. Under such assumptions the speed for best climb would be the same as the speed for minimum sink and in both cases lower than best glide speed.

Nevertheless mentioned Cessna converts fuel to mechanical energy through not-so-magical fixed pitch propeller which pushes some amount of air around. Such propeller would be typically optimized for highest efficiency at the cruise speed, so with decreasing speed the amount of available mechanical energy dereases. Which results in changed shape of power curve and maximum point moves towards higher speeds compared to the "unpowered" power curve.

This shift can be high enough that Vy ends up higher than Vg.
The Vy is always higher than the speed for the best climb angle, because these two speeds are found on the same (max power) power curve. For the same reason best glide speed will be always higher than speed for minimum sink. But speeds for best rate of climb and for the least sink does not need to be the same because of effects of real propeller.
For related images and more information, have a look at great online text See How It Flies.

+1 for whipping out your pen in two colours no less, making charts, and taking pics with your phone.  Well done.

To add: Vx is the speed for the steepest climb whist Vg is the speed for the shallowest glide (best glide speed). Flying at Vx or Vg yields the best angle. Flying at Vy yields the best rate of climb at a more shallow climb angle.

Re "propeller would be typically optimized for highest efficiency at the cruise speed", there are also fixed-pitch propellors that are optimized for climb, which you might see on bush planes and the like.

This is great answer but it could be further improved.  In the first sentence when you mention the "power curve for an unpowered airplane", you could make it clear that what you are really talking about is a graph of airspeed versus sink rate.  You could then explain that this also equates to power-required curve if we want to add power to make that airplane maintain level flight.  You could also point out that the real essence of the answer is "the power-available curve is not a straight horizontal line, and therefore the shape of the power-required curve is not the only factor at play."

The fact that best climb speed is above best glide speed indicates two things:

The airplane has a fixed pitch propeller.
Its power at climb speed is limited by engine RPM limits.

Normally, best climb for propeller aircraft should be when the ratio ${\frac{c_L^3}{c_D^2}}$ reaches its optimum which is at higher lift coefficients than best glide. But that not only assumes a quadratic polar but also a constant propeller efficiency over speed.
A fixed-pitch propeller has its pitch normally selected for cruise so in climb the aircraft will fly slower than what the propeller is designed for. At that speed, propeller efficiency increases almost linearly with speed, as can be seen in the plot below. To create it, I simply calculated the angle of attack and dynamic pressure at 75% span and with that approximated the thrust. Next, I used the same figures for calculating the drag on the blades and thus the power required to drive them at that speed. Dividing thrust times speed by that power produced the efficiency graph. Note that I used the advance ratio (forward speed divided by circumferential speed at the tips) for the X-axis.

The linear increase in efficiency will in effect produce constant thrust over speed, so the best climb speed should be the same as for turbojets.
But that again makes assumptions which might not hold in reality. Obviously, it assumes constant power and prop RPM over speed. If the prop cannot absorb the available power at lower speed, the engine has to be throttled back in order to avoid overspeeding it. I would expect that you cruise that Cessna at a more forward throttle position than what is possible in climb.
Now we have a condition where power and thrust both increase with speed, so the best climb speed is above best glide speed.
Thank you for pointing out this seeming contradiction! It made me reflect my assumptions in deriving best climb speeds and helped me to refine my conclusions.

C172 climbs at Vy on full throttle. At higher speeds (incl. cruise) it has to be throttled back.

@Zeus Then why would v$_y$ be above best glide speed? The accepted answer does not explain this – maybe you can? What is the RPM in climb?

There are different versions, some (cruise optimised) have redline at 2300 RPM, some at 2700. At Vy (76-79 KIAS), both are a bit short of redline (these aircraft are very forgiving and you need to work or be really negligent to exceed limits). They start to overspeed (at full throttle) above 85-90 KIAS. So, in our speed range of interest it does appear to be power-limited. But cruise speed (~110 KIAS) is outside of this range.

I think there is a typo in the second sentence of the answer.  You stated that best rate of climb should occur at max (Cl/Cd)^(3/2).  Didn't you mean to say the maximum value of (Cl^3 / Cd^2) ?

@quietflyer: Thank you for your diligent proofreading. Corrected.

Agree with comment from Zeuss.  Obviously this answer has a lot of good stuff in in it but this is a significant issue that should be fixed, specifically re " I would expect that you cruise that Cessna at a more forward throttle position than what is possible in climb."  Perhaps I have the advantage of having only a relatively small handful of powered a/c types occupying my memory cells but this issue re the Cessna 172 comes quickly to my attention...

@quietflyer: Since prop efficiency increases linearly with speed, the best climb speed would be at best L/D. Now the question claims it is higher, so there must be some extra power or efficiency gain at increasing speed. Where does it come from?

It seems we have a can of worms that is not yet unraveled.  I thought my answer shed some light on these questions, but perhaps not truly adequately.  That's all I have for today;  more later...

If we take the curves for power required and power available, the best glide is the airspeed at which a straight line from the origin is tangent to the power required curve.
And the speed for best rate of climb is the airspeed at which the tangents to the power required and power available curves are parallel...
From 'Theory of Flight', by Richard von Mises (Dover Books):

Hence, with properly shaped curves, and in theory at least, the best climb speed might be higher than the best glide speed...

That does not explain why, it only repeats what has been said before.

It explains how, and that's what the OP asks...

Good answers have been posted, but here is another spin that adds a few other important points, while omitting for brevity some of the other points that have already been made.  This answer also clears up a misconception in the original question about the significance of the Lift/Drag ratio in relation to the airspeed for best glide ratio and the airspeed for minimum sink rate.
For unpowered flight, we can draw a curve of sink rate versus forward (horizontal) speed.  (Some other answers have referenced this as a "power curve".)
In unpowered, non-turning flight, Lift, Drag, and Weight form a closed vector triangle.  Since the Lift and Drag vectors act perpendicular and parallel to the flight path, respectively, this closed vector triangle "anchors" the direction of the flight path in space with respect to the Weight vector.  In other words, if we know the direction of the flight path with respect to the ground-- i.e. the glide angle-- then we know the L/D ratio, and vice versa.  In fact, in unpowered, non-turning flight, the glide ratio (horizontal distance travelled per unit of altitude lost) is always exactly the same as the Lift/ Drag ratio.  This means that glide angle = arctan (D/L).
This means that the smallest (i.e. flattest) glide angle takes place at the minimum D/L ratio.
Starting with a graph of sink rate versus horizontal (forward) speed, there's an easy way to find the "glide ratio", or horizontal distance traveled divided by altitude lost, for any given horizontal speed.  It's simply the slope of the line drawn from the origin of the graph to the point in question.  The highest possible "glide ratio"-- which corresponds to the smallest possible "glide angle"-- is simply the point where a line drawn in this manner is exactly tangent to the curve of sink rate versus forward (horizontal) speed.  And as we've already noted, in unpowered flight, the "glide ratio" at any given forward (horizontal) speed is also exactly the same as the L/D ratio at that speed, so the highest possible glide angle also occurs at the forward (horizontal) speed that gives the highest L/D ratio or lowest D/L ratio.
Note that this tangent point will always occur somewhat to the right of the point of minimum sink rate.  The speed for the flattest glide angle (best glide ratio) is always somewhat faster than the speed for the minimum sink rate.
For reasonably flat glide angles, forward (horizontal) speed is nearly the same as airspeed.  Therefore, for most practical purposes, our graph of sink rate versus forward (horizontal) speed can be re-labelled as a graph of sink rate versus airspeed.
Recall again that the smallest (i.e. flattest) glide angle takes place at the minimum D/L ratio.  For reasonably flat glide angles, as we vary airspeed, lift remains nearly equal to weight, so nearly all the variation in the L/D ratio (i.e. the glide ratio) is due to variation in Drag, not Lift.  (Don't misinterpret this to mean that the lift coefficient stays nearly constant as the airspeed varies-- it does not.)  This means that for reasonably flat glide angles, it is a close approximation of reality to say that the airspeed that yields the minimum D/L ratio and the smallest (flattest) glide angle, is also the airspeed the yields minimum Drag force, as measured in pounds or Newtons.  (Don't misinterpret this to mean that the drag coefficient is minimized at this airspeed-- it is not.)
Therefore, at the forward (horizontal) speed, and the airspeed, that yields the minimum sink rate, the Drag force is actually higher than it is at the airspeed that yields the maximum glide ratio (minimum glide angle).  Here's one way to think about this-- loosely speaking, the Drag force determines the steepness of the "slope" that the aircraft is gliding down.  But travelling more slowly along a slightly steeper slope will give a lower rate of descent than travelling more quickly along a slightly flatter slope.
What happens if we start with a sink rate-versus-airspeed curve generated by an aircraft with the prop removed, or with the engine generating just enough power so that the prop is contributing exactly zero net thrust, and then we change the conditions so that the prop is windmilling and forcing the engine to turn?  The sink-rate-versus-airspeed curve will be degraded-- the sink rate for any given airspeed will be increased, but more so at higher airspeeds.
 The point of minimum sink rate, and the point of flattest glide, will both be shifted toward the left, toward lower airspeeds.
To maintain level flight, the motor has to supply enough power to offset the sink rate that the aircraft would experience if the motor were contributing zero net thrust.  More precisely, the power requirement is equal to sink rate times weight.  Therefore our graph of sink rate versus airspeed can also be thought of as a graph of "power required" versus airspeed.  However, to look at how an aircraft will perform when we add power, the appropriate "power required" graph would be one generated with the propeller removed (or with just enough engine power applied to produce exactly zero thurst), not one generated with the propeller windmilling.
At any given airspeed and throttle setting (e.g. wide-open throttle), the sink rate or climb rate will be due to the difference between the "power required" and the "power available".  At the wide-open throttle position, if the graph of "power available" versus airspeed were a simple horizontal line, then the shape of the "power required" graph-- which is the sink rate versus airspeed graph-- would entirely determine the the airspeed for maximum climb rate.  In this case, the maximum climb rate would always occur at the power-off minimum sinking speed-- at least so long as we were talking about a sink rate versus airspeed graph that was created with the prop removed or idling in the zero-thrust condition, rather than windmilling.
However, the shape of the power-available curve is not a simple horizontal line, especially in the case of an aircraft with a fixed-pitched prop.  It will typically have a peak that is located well to the right of (i.e. higher than) the airspeed for the best glide speed or max L/D ratio, which biases the speed for best climb rate toward a higher airspeed.
In summary, the best climb rate occurs at a higher airspeed than the flattest glide angle because--
1) the airspeed for flattest glide angle is measured with the prop windmilling, not with the engine applying just enough power to generate a zero-thrust condition.  This shifts the sink rate-versus-airspeed curve toward the left of where it would be if it were generated with the motor creating just enough power so that the prop were contributing neither thrust nor drag.
and
2) the power-available versus airspeed curve is not a flat horizontal line, but rather peaks at an airspeed that is higher than the airspeed corresponding to the flattest glide angle.  With a fixed-pitch prop, this is typically is true even if we are making a comparison to the aircraft's performance at the airspeed that gives us the flattest glide angle with the engine providing enough power to generate a zero-thrust condition, and it is even more true if we are making a comparison to the aircraft's performance at the airspeed that gives us the flattest glide angle with the engine windmilling.  This biases the best climb-angle and best climb rate airspeeds toward the right (toward higher airspeeds) compared to what we'd see if the propulsion system delivered the same amount of power at all airspeeds.
Two final notes--
A) All discussions of glide angle in this answer are with respect to the airmass, not the ground.  In other words, if we're measuring our glide angle with respect to the ground, then we're doing so in zero-wind conditions.  Optimizing the choice of airspeed to fly to get the best possible glide angle over the ground various wind conditions is an interesting topic, but one that is beyond the scope of this answer.
B) This answer has only touched briefly on the subject of lift and drag coefficients.  It may interest the reader to know that the following are true, using "Cl" to represent the lift coefficient and "Cd" to represent the drag coefficient:
i. The airspeed for max L/D ratio is also the airspeed where the ratio of Cl/Cd is maximized.
ii. The airspeed that yields the minimum sink rate is also the airspeed that yields the maximum value of (Cl cubed) / (Cd squared).
iii.  The expressions (Cl/Cd) and (L/D) are equivalent, but the expressions ((Cl cubed) / (Cd squared)) and ((L cubed) / (D squared)) are not equivalent.


text:
How can a plane fly far longer than designed?
The current record for longest commercial flight is 21,602.22km by Boeing 777-200LR.
However the designed maximum range for B777-200LR is 15,800 km. So how is this possible?

You may find this question, or better the answers below it, helpful.

The design range is fully loaded.  This flight had 35 passengers, no cargo, full fuel and was run as a project and flown by a test pilot.  It was not a commercial flight in the meaning that most people would recognise.
They had to wait for weeks until the winds aloft, especially the jet stream, were at their most advantageous.

and they used higher-density fuel. See here (PDF) for specs.

The designed maximum range is just a number, it is affected by a number of constrained factor like fuels and payload as wells as unconstrained factor like jet-steam.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
How are pitching and rolling moments transferred from rotor to the body?
When a rotorcraft pilot moves pushes on the cyclic control stick, the swashplate tilts so that angle of attack of the retreating blades increase and of the advancing blades decrease, which creates forward pitching moment on the rotor (shifted 90° due to gyroscopic effect).
Now the first reaction is that the blades flap up aft and down forward, tilting the plane of rotation forward. But which is then the dominant effect that makes the helicopter body to follow the pitch?

Is is the blades pulling on the hub due to centrifugal force trying to align it with their own plane of rotation,
or is it that the lift vector tilts with the rotor so its action line no longer passes through the centre of gravity?

A good way to think of it is with a teetering system, you fly the rotor disc here and there and the machine itself is just slung under it like a ball on a string that follows wherever the forces take it. Articulating rotor is a bit like the body is connected to the rotor disc by a flexible rod instead of a string, it still tilts and flies around as you command it, but it also imparts some of its tilt to the body. Articulating masts and the transmission mounts have to take bending as well as lift loads, whereas teetering sees no bending loads, unless you get into mast bumping, and you're dead.

Related - - https://aviation.stackexchange.com/questions/38859/why-does-the-helicopters-nose-go-down-when-the-cyclic-is-pressed-forward-in-a/38904#38904 --even with a teetering system, the helicopter does not just dangle freely from the rotor disk -- see last paragraph for detailed explanation.

@quietflyer, that answer was (the answer is deleted now) already linked below. I already read it, and it definitely does not say that. What it does say is that when the body tilts, it will make the rotor tilt too. That is clearly important to prevent the rotor hitting the body, but because the moment is between the rotor and air, it does not create any moment on the body. The body does actually “dangle freely” (on teetering rotor), though that's not really a good term, because it evokes a fixed mount, which the rotor definitely isn't.

@JanHudec -- so you disagree with the following?  (Highly condensed from the link above)  --  (With hinged rotors) "As soon as the rotor plane changes as a result of cyclic stick input, the resulting rotor hinge moment will change fuselage angle accordingly, providing the desired feedback cue." "With teetering rotors, there is an indirect aerodynamic coupling between fuselage and rotor shaft. This provides the same cues as the hinge offset solution but at a slower rate."

@quietflyer, yes, I disagree with that. The aerodynamic coupling in case of teetering rotor (it exists for every rotor anyway) is from body to rotor only, because the actual force is between rotor and air and the body position only affects cyclic. Of course the effect of rotor tilt on the body is there, but the discussion is now what effects there are besides that. And it does have practical implication too: teetering rotor loses all control effectiveness when unloaded, hinged or flexible maintains some.

@quietflyer, the link certainly is related, but it answers a different question of ‘what ensures the tilt between rotor and body does not exceed some reasonable range’ (with, basically, ‘the way cyclic is rigged’).

@JanHudec -- thanks for the note; not being that knowledgeable about helicopters perhaps I placed too much reliance on that linked answer

The impact of these effects depend on the rotor design.  E.g. a teetering rotor only includes the second effect you mentioned (tilted thrust vector), the 1st effect is absent.  The first effect you mentioned increases as the "flap hinge" is moved away from the hub, giving more control force utilizing CF.  You may be interested to know there's typically a 3rd effect - if the blades are restrained from flapping freely (in the simplest case a spring) that restraint creates a pitch moment about the hub which also pitches the aircraft.   Each of these is discussed here.

@Koyovis, I am probably missing something, but that explains why the rotor wants to return to aligned with the fuselage, not why it pulls the fuselage to where it's turned.

@JanHudec The rotor disk and the fuselage want to align relative to each other. The pilot commands the rotor disk angle to speed up, this is the offset in the coupling. Yes the fuselage exerts a moment on the rotor as well, but the pilot has control over the desired disk deflection.

@Koyovis, so there is absolutely no disagreement then. For teetering rotor, the angling of the lift is the only effect that applies moment to the fuselage exactly as this answer states (and then the relative angle subtracts from the cyclic command, which prevents the rotor tilt from running away, which is interesting, but orthogonal to the question).


text:
Why is the total count of people on a plane given as the number of 'souls' on board?
Why don't they just say 'people' on board, why souls? What is the origin of this term? I'm thinking it comes from sailing as I think I've heard that term in reference to crews out at sea, but I'm not a sailor so I don't know.

Because the autopilots don't have souls... not yet anyway.

@RBarryYoung Except Otto.

I suggest a secular alternative as number of hearts on board, if anyone needs.

@user13107 no one mentioned religion, although as a Christian I believe everyone has a soul, your alternative wouldnt satisfy the disambiguation of transporting dead persons or people.

Is "souls" used outside the United States? I've never heard it used in Australia. It sounds odd and has superstitious connotations.

don't know @MarkyMark

Although I don't have a reference, I believe the term is developed in connection to "Save Our Souls", a commonly believed (but mistaken) meaning of Morse-Code S.O.S.   When someone receives an SOS, they then ask, "how many souls need saving?"

Infact this is just a US think, most other places in the world will talk about POB (people on board)

The primary reason is probably that it ensures there is no confusion between passengers, crew, or infants. Technically, "passengers" is the number of seats occupied, "crew" is both the pilots and flight attendants on duty. So any small children brought on as "lap children" will not be included in the "passengers" count, but should be included in the total number of people on board.
I found another interesting point over on the English Stack Exchange site, which is that dead bodies are sometimes transported as well. In this case, some might consider these "people" as well. Also, in an incident, the bodies should not be confused with the regular passengers.
So, "souls" effectively communicates the number of living humans on board.
There may certainly be holdovers from the maritime influences on aviation as well.

Does the number of souls include (live) animals being transported on the plane?

Interesting, never gave this any thought before.  Do unborn children count as souls on board too then?

@BrianKnoblauch without getting into the theological implications, no: Unborn children are not counted as souls on-board for ATC & Rescue purposes. Neither are pets (everyone knows cats are instruments of the devil), but if a pilot has time to inform ATC that there are live animals on board it's good to convey. A response to "Say souls on board" might therefore be N12345 has 19 souls, 2 cadavers, and a dog.

and corpses are on the cargo manifest, not on the passenger manifest. So no confusion there either. (got that while working for the cargo department of an airline for a bit long ago).

Corpses are only on the cargo manifest if they were dead when loaded. What happens to the "souls" count if someone dies (e.g. of a heart-attack) in-flight, and then the plane runs into unrelated(?) trouble?

@Fixed Point, No, though on general aviation flightplans, it is not uncommon to see dog on board, or similar in the remarks on a flight plan, to make sure that rescue crews don't associate the dog as a passenger/crew member when doing emergency rescue operations.

I flew loads of cadavers, back in the war. But this plane has live souls. It's an entirely different kind of flying, altogether.

@RobertColumbia Surely you can't be serious?

I agree with what fooot said.  Also, I would add, as someone to volunteers in search & rescue (Civil Air Patrol) as a mission pilot, when you hear the word "souls," it adds some urgency and seriousness to the handling of any emergency.  When an air traffic controller asks a pilot, during an emergency, for the number of souls on board, it communicates to the pilot that the controller and pilot are focusing extra hard together on solving the emergency successfully, and that one word tells the pilot that the controller is going to be marshalling resources to help in every way possible.  "Souls" is a term full of life and caring.  For rescuers, it communicates very quickly the total number of persons who must be found and saved.

The earliest reference I can find to 'souls' as a count of persons is mid-eighteenth century, although it probably was in use earlier. It appears in maritime commerce, as the number of living humans aboard a ship, and in civics, as the population of a town or city.
I think that in the early 1700s the words 'people' and 'person' both had strong connotations compared to those words today. 'People' meant humans of a certain country or a specific culture, and 'persons' meant humans of note or important characters.
So I conclude that a need arose, driven by government and commerce, for a word to mean an unaffected and precise head count, that yet afforded those being counted a little more respect than the barrels, boxes, coins, and cows whose numbers were also tallied.
Now if I could find a reference to that usage of 'souls' from the thirteenth or fourteenth century, I would simply assume that it arose from the learned churchmen who were doing the counting, as literacy was not yet widespread.

There is a reference to the 14th century use of the term here: http://english.stackexchange.com/a/97556

In relation to population of a town or city I believe it was also used by Russian gentry and aristocracy (in translation at least -- I don't know the term in Russian). "I have 100 souls" means there are 100 serfs bound to my estate. I always took it to imply to some extent 100 souls "in my care", which of course to me as a member of a culture without serfdom seems disingenuous. But in that sense it has the same resonance as the crew of a ship/plane talking about souls on board. So I speculate it may be a synecdoche emphasising the part of the person most worthy of care.

What about women and slaves? Were they counted as souls in maritime commerce at that time?

The term Soul appears many times throughout scripture, Hebrew translation of this particular use and meaning is literally "breather." Some are on the right track with anatomical heart as this is what is required to circulate oxygen. This also clarifies why transporting deceased persons are not counted among SOB. They are no longer breathing.

Aircraft (and previously, ships or trains) are frequently used to transport casketed remains en route to funeral. "Souls" was devised to remove any ambiguity about which "passengers" were among the living.

nope, those are not part of the passenger manifest. They're strictly counted as cargo (though very special cargo, and there are procedures in place to ensure respectful handling at all times, including special storage facilities at airports, hearses, etc.).

It used to be "souls on board", but was frequently abbrievated to 'sob's", which somehow didn't sound right.  It is now "persons on board"; but there's a lot of momentum in the aviation business and "souls on board" is still used by many

Do you have a citation for these claims? And what is the origin of the term, which is what the question actually asks?

The term "soul" once meant a whole person: body and spirit. Thanks to Hollywood's love affair with the word, most now believe it means spirit.
The sad result of this is several phrases now have a different meaning than the historical writings that contain them once intended.
"not one soul was saved" - everyone died, now means they are all dammed
"bless his soul" - may he have a long life (literally blessing the integrity of the body and spirit), now means bless his spirit
"soul mate" - a person physically and spiritually matched, now means a single special someone that is primarily a match of the spirit
"he sold his soul" - he has given his life to evil, now means a state of evil that primarily affects the after life
"bare one's soul" - to share the intimate details of once physical and spiritual life, now means to reveal primarily emotional details as a stand-in for spiritual things
"rest his soul" - implying that sleep is symbolic of death, now solely a blessing on the spirit
"lost soul" - a person not doing well physically and spiritually in this life, now means a person not following spiritual paths


text:
How far can a passenger plane taxi?
Most commercial flights will have to taxi a short distance to the end of the runway, before actually taking off. But in an absurd, absolutely extreme case, what if that passenger plane could only taxi, not fly? How far would the plane be able to taxi before it runs out of fuel?
I imagine that the answer is in the ballpark of "many times around the world", given that passenger planes like a Boeing 777 or Airbus A380 hold tremendous amounts of fuel. However, since no plane has ever taxied until it has run out of fuel, I ask this question from a theoretical standpoint. I certainly wouldn't want to be on a plane taxiing the entire route from Los Angeles to New York!

If you ever land on one particular runway at Amsterdam Schipol you'd be forgiven for thinking they must have loaded more fuel just for the taxi to the ramp!

@Jamiec I always joke we must've landed at Rotterdam/The Hague airport by mistake when that happens - it's a 20 minute taxi at least! (which is half the time it takes to get from EHAM to EHRD by car)

I've spent more time taxiing around ORD than it took to fly there from GRB.

@Jamiec They do load more fuel. There's always a taxi allowance in fuel calculations

@TomMcW Taxi fuel is for taxi out, not in. So it"s spent before take-off. There is no fuel calculation for taxi after landing.

The number will vary depending on the aircraft type & installed engines (how much fuel it holds, and how much fuel it burns per hour at taxi speed), but the ballpark figure is "Much less than the range in flight", because the specific fuel consumption figures (how much power, and thus distance, you get per unit of fuel burned) are less favorable during taxi than at cruise.

To work an example I used the numbers for an A320 taken from here and not checked it burns 270-330kg/hr (depending on the engines installed) so let's split the difference and say 300kg/hr as an average.
The A320 can hold around 15,000kg of fuel, so doing the division it could run its engines at taxi power for around 45 hours.
If we assume a taxi speed of 20kts for 45 hours the aircraft could theoretically taxi 900 nautical miles (1036 statute miles, or 1667km), a little less than one-third of the range in flight.

That would need several crews ;-) Would parts of the aircraft bear this long taxi (e.g. tires)?

You'd be hard pressed to find roads suitable for going a thousand miles without hitting something, as well! Maybe in Australia...

And I would taxi 500 miles and I would taxi 500 more just to be the man who'd taxi 1000 miles to park outside your door.

@mins That is a good question: 45 hours is probably shorter than the landing gear service intervals (tires, bearings, breaks, etc.), and while these aren't "continuous duty" items the loads imposed by taxiing are probably lower than the takeoff/landing loads, so I would imagine the gear can handle it, but I'm not sure how it all works out for continuous loads...

@MikeClark Lmao!

You do not need a pilot to taxi, a technician can to this (assuming without intention to fly).


text:
What is the safe speed to use highspeed turnoff?
I understand that high speed turnoff is for the plane to exit the runway asap. What is its design specification and how fast can a plane use highspeed turnoff? Assuming only A320,737 and larger.

I don't have a reference, but I have always been told that high speed turn offs are designed for 60 knots, assuming a dry uncontaminated surface.

are all high-speed turnoffs at the same angle to the RW? 30 degrees? 45?

Okay safe speed to be a blanket and highly dependent on the type of plane. How about the disign aspect? 30 or 45 degree? How wide it must be? Any special marking? Out of memory answer is fine by me.

Please be careful applying a blanket figure during high speed turnoff. There are many variables which you should consider. These are:
•   Exact angle of the taxiway(you're turning onto):  If it's a very shallow angle off the runway and therefore does not require much turning, high-speed turnoffs are easier and manageable, and vice versa.
•   Rate of deceleration
•   Side load limitations on the CRJ
•   Tolerance of the nose gear
•   Traffic situation on taxiway
Generally speaking you need both sets of eyes outside, especially if you are joining or crossing another Taxi Way.

According to AC 150/5300-13A, section 409:

b. High-speed exit taxiways. A specific case of an acute angle runway
  exit taxiway that forms a 30-degree angle with the runway centerline
  is commonly referred to as a “highspeed” exit taxiway. The purpose of
  a high speed exit is to enhance airport capacity.

Since the parameters of high-speed taxiway design is the angle at which the taxiway intersects the runway, and does not take into account the aircraft speed, then the answer will be different for every aircraft.

From the Jeppesen glossary, page 14 of this PDF:

HIGH SPEED TAXIWAY / TURNOFF (HST) — A long radius taxiway designed and provided with lighting or marking to define the path of an aircraft, traveling at high speed (up to 60KT), from therunway center to a point on the center of a taxiway. Also referred to as long radius exit or turnoff taxiway. The high speed taxiway is designed to expedite aircraft turning off the runway after landing, thus reducing runway occupancy time.

Can you provide a link to where this came from?

Well, @fooot, he did provide some sort of reference jeppessen page 76 GLOSSARY, but a link would have been much nicer. Does Jeppessen put out more than one document? (Rhetorical question.)


text:
Sukhoi Superjet 100 avionics
The Sukhoi Superjet 100 features flight control system with characteristics copied from Airbus. Side-sticks, same control laws. But does it actually use any of the hardware or software from Airbus (under license), or is it an independent development based on detailed descriptions of the behaviour?


text:
Since which moment do the Low Visibility Procedures apply?
For CAT II and CAT III approaches require that protected area around the ILS antennas is kept clear from obstacles so it does not disrupt the ILS signal.
So when there is an airplane on the final approach, at which moment at latest must the protected area be clear (which includes the preceding aircraft must be out of it)? Before the landing aircraft reaches 1000' above (stabilized criteria)? Or before it reaches CAT I minima? Or even further out?

ICAO Annex 10 Vol. 1 provides some general guidance on ILS critical and sensitive area protection:

2.1.9.3 Technical and operational logic associated with critical and sensitive areas. Ideally, the critical area is
enforced during all ILS operations with protection afforded down to at least the Category I decision height. A critical area
disturbance would normally impact all aircraft using the ILS signal at a given time (entire approach). [...] From an operational perspective, the sensitive area would ideally protect aircraft operations at
least from the Category I decision height down to the runway, and be activated during low visibility conditions only (e.g.
Category II and III). [...]
Note.— Guidance on operational procedures for the protection of critical and sensitive areas is provided in ICAO EUR
DOC 013, “European Guidance Material on All Weather Operations at Aerodromes”.

(ICAO Annex 10 Volume 1 "Radio Navigation Aids", bold emphasis mine)
The referenced document contains some more details, first on when LVP apply in general:

7.5.6 LVP Operations Phase
7.5.6.1 The point at which LVPs are in force must be clearly defined in terms of a specific RVR
and/or height of cloud base and must be promulgated in the LVP. LVP should be in force at
the latest when the MET conditions deteriorate below RVR value of 550 m and/or cloud
base of 200 ft for approach and landing operations and below RVR value of 550 m for
departure operations.

(ICAO EUR Doc 013, bold emphasis mine)
And then further on ILS operations: the critical areas should always be clear and the sensitive area should be clear at the latest when the landing aircraft is 2 NM before the threshold (recommended is 4 NM when possible or no radar available):

7.5.6.4 ILS operations
7.5.6.4.1 To ensure that the integrity of the guidance signal radiated by the ILS is maintained during
aircraft approaches, all vehicles and aircraft on the ground should remain outside the ILS
critical and sensitive areas. The ILS critical areas must be clear of all vehicles, persons and
aircraft at all times.
7.5.6.4.2 These objectives are normally achieved by providing appropriate spacing between
successive landing and/or departing aircraft. [...] To accord with the basic
requirements, the spacing specified should provide sufficient separation between successive
approaching aircraft, normally to allow the leading aircraft to land, to vacate the runway,
and to clear the ILS localizer sensitive area before the following aircraft reaches a point
2 NM from touchdown. [...] At aerodromes where the traffic density is low or
where the range of the approaching aircraft cannot be monitored by radar, the separation
should be increased to enable the leading aircraft to clear the runway and ILS localizer
sensitive area before the following aircraft reaches a point 4 NM from touchdown, i.e. about
the position of the outer marker (or equivalent DME position).

(ICAO EUR Doc 013, bold emphasis mine)


text:
How to change 737 Max to 737 NG?
With the on going grounding of 737 Max, if some airlines want to change their 737 Max to 737 NG what modification is needed? The main change would be the engine and control system. Any other change is needed in order for the plane to be re-certified for flight?

Probably they would have to do full certification flying program which is very expensive!!! And who wants NG instead of Max? If Max never flies probably the best option is to remove engines and scrap the rest.

Such a certification program is not just very expensive, it also takes a long time! Probably much longer than the re-certification of the MAX, which has the more efficient engines that airlines want anyway...

@Bianfable re-certify the MAX as much as you want. Most people will refuse to fly in one anyway.

@QuentinH I doubt that. With fixed MCAS logic there is no reason to assume the MAX is less safe than any other airliner. It might actually be safer because they are taking their time now to check everything very carefully. And passengers usually cannot really pick which aircraft they want to fly in anyway, they just care about cheap prices.

Nice question from aircraft design point of view. Retrofit to an older design is a challenge, that worth further discussion.

I'm curious if there is any way for Boeing to recover some costs from the hundreds of MAXes they have sitting around, in the event the MAX is never able to fly again. Would it be feasible for a manufacturer to have a conversion program for MAX -> NG?

This page lists all the functional differences between the MAX series and the previous 737 variants. There are quite a bit of substantial changes like the reshaped tail cone and electronic bleed system. Not only are the engines different but the mounting pylon was changed to account for the new engines so you likely cant just "bolt on" the old engines. Even the cockpit has a different panel.


text:
Lufthansa making short flights MUC→LEJ→PRG→VIE→MUC with A380s
Today I noticed a Lufthansa A380 taking off from Prague and … flying to Vienna. And the FlightRadar track looks like it didn't even stop here. It starts with the plane turning off the runway at the end, shows it taking half an hour to taxi back to the beginning and taking off again. And yes, the track immediately follows the one for the flight from Leipzig, which in turn suggests it didn't stop in Leipzig either.
Looking up the flights LH9860, LH9861, LH9862 and LH9863 shows that they've been flying that short loop regularly for at least a couple of days with two different aircraft.
Does anybody have an idea why they are doing these flights?

It must be crew training as part of bringing the A380s back into service?

The vast majority of training needs for any aircraft type is for takeoff and landing - how to configure for takeoff, when to reject a takeoff, when to go around when attempting to land, etc. It would be a waste of time (and fuel and labor costs) to use 4 hour flights for refresher training.

My guess is they're trying to retain their landing slot rights. If they don't use their slots in a certain timeframe, they can be forfeited. This may be combined with A380 training and test flight requirements at the same time.

@user71659, no, it's not about landing slots, because they never operated an A380 to Prague and I don't think they want to; it's not an important hub. The only airline that operated an A380 here was Emirates (to Dubai) and they've switched to a 777 some time ago.

@JanHudec No, the size of the airplane generally doesn't matter when it comes to landing slots. That's the whole point of the A380, it consumes 1 slot, the same as the 777, while carrying ~35% more passengers. That's exactly why I said it's merged with training.

Lufthansa is currently in the process of re-activating four of its Airbus A380s, which were placed in storage during the pandemic. Part of this process is re-training the pilots, partially in the simulator, but also with training flights in the real aircraft:

But before the four reactivated Lufthansa Airbus A380s can take off from Munich again, the crews have to be retrained. This also happens in the simulator. Flight training will also follow in May [...]

(aerotelegraph.com, in German, translated by Google)
The first training in May included touch-and-gos at Leipzig/Halle as well as several short flights:

The cockpit crew of Lufthansa's first reactivated Airbus A380 practiced a total of ten touch-and-go maneuvers in Leipzig/Halle. [...]
There are said to be plans for a route that also includes two landings abroad. Accordingly, it is planned that Lufthansa's A380 will fly the following route: Munich - Leipzig/Halle - Berlin - Dresden - Prague - Vienna - Munich. [...]
According to the information, this route will be flown eight times in May, presumably also with D-AIMK.

(aerotelegraph.com, in German, translated by Google)
These training flights in May have also been announced by Lufthansa News on Twitter:

Next on the #A380 D-AIMK Training-Flightschedule: 03.05.2023 FRA-LEJ (LH9860): 10:00 LT, LEIJ-PRG (LH9861): 11:10 LT, PRG-VIE (LH9862): 12:00 LT, VIE-MUC (LH9863) 12:45 LT.

(twitter.com)
I'm not sure if they also announced the training flights in August, but two more A380s will be re-activated in October, so it makes sense to start the training now:

In addition, a daily connection from Munich to Los Angeles will be available from October 5th - and from October 28th we will offer you daily flights to the vibrant Thai metropolis of Bangkok.

(lufthansa.com, in German, translated by Google)
Another two A380s will follow in 2024 (aerotelegraph.com), so we can expect to see some more of these training flights over the coming months.

It's still the same flight numbers, just the time has shifted to the evening.

Would there be any passengers aboard during these short hops?

@Landak No, they didn't even go to a gate after landing at their intermediate stops. They just taxied back to runway to takeoff again.

These flights are for revalidation of crew licenses.
Lufthansa is resuming A380 operations, after a 3-year long break. Since their pilots didn't get to fly, their licenses lapsed.
Most of the renewal training can be done in the simulator, but a few take-offs and landings have to performed on the real aircraft. To do this, Lufthansa makes tours of short flights around their  A380 base to efficiently get their pilots final part of the re-training done. I assume they switch partial crew in-flight and/or during taxiing.


text:
What would be the hazard of raising flaps on the ground?
I was reading ASRS report when I found something I don’t understand. What would be the hazard of raising flaps on the ground? What bad thing can happen?

However, with all the activity around the aircraft, including refueling, it was not safe to raise the flaps. I elected…not to raise the flaps until the area cleared.

https://asrs.arc.nasa.gov/publications/callback/cb_482.html

Without knowing what type of aircraft was involved in this incident, it is hard to tell. But, in general, a moving flap would provide a pinch point for any personnel in the area. Considering the article mentions that the hydraulics were in the on position, there would be a possibility of crushing a body part of maintenance personnel.

Later on, the same ASRS report says

the refueling truck struck a flap fairing when departing

Thus, the deployed flaps were low enough that raising them would risk hitting someone or something.

We may not be able to learn the aircraft's type, because

ASRS’s award winning publication CALLBACK is a monthly safety newsletter, which includes de-identified ASRS report excerpts with supporting commentary in a popular “lessons learned” format.

If they include the date (even the rough date) of the incident, searching avhearld or the FAA site in that time frame should turn up the actual incident in question. Other details of the event could be used if a date isn't provided. It may not be easy, but it could likely be done.

@FreeMan, this incident wouldn't be on AVHerald: it involves a parked aircraft and no danger to passengers.

There's got to be documentation on it somewhere, @Mark. I was just pointing out that even though CALLBACK doesn't give the specific info, there may be enough clues available to track down the specific incident if someone really wanted to know. Not suggesting it will be easy, just that it's probably possible.


text:
What is the T and the I in dispatcher language?
From October 2019 ASRS CALLBACK, a captain told a story when the dispatcher

told me, “All the ‘T’s had been crossed, and all the ‘I’s had been dotted: everything has been done the right way, routine... etc.”

What is the ‘T’ and the ‘I’ mean in this sentence? What is their significance?

It's referencing an idiom. Or are you asking about what the dispatcher would have actually done?

Hah it is English word, not aviation specific. Yes this is the answer I want. So the dispatcher means he alr do every thing needed for the flight. Thx a lot

This would probably be better suited for English, as it's a phrase that really has nothing to do specifically with aviation. However...
Having dotted your "I"s and crossed your "T's means that you've paid attention to all the details, that you've finished everything that needs to be done, the job is complete.
An uncrossed "T" could be a capital "I" or a lower-case "L". An undotted "I" could be a lower-case "R" or "E". These are especially true of hand-written, cursive letters. So crossing your "T" ensures clarity and completes the job.
When the dispatcher said this to the captain, he was telling him that he'd gone over all the details and the job was done.


text:
What are the process involved in tire rotation during long term storage?
During Covid-19 crisis in 2020 a lot of planes are grounded for a long time. Tires of parked planes can develop flat spot hence the need to keep these tire rotate. What are the processes involved regarding tire rotation during this time?
Is the plane towed 100 feet every week or rotate each tire 45 degree every day or something else?

Aircraft with tire marking.
Source: https://www.facebook.com/media/set/?set=a.1908245919474139&type=3


text:
Why do you have to put the blinds up during take off and landing?
I understand the rationale for putting seat backs straight, folding tables, fastening seatbelts etc., but I've never really understood why the window blinds matter.

That are the two most likely times there can be an incident, and its a usual policy to have blinds up during those stages so passengers can also spot and alert the crew if any outside malfunction goes undetected.

@Iceman: "Stewardess? Oh, stewardess!? I hate to bother you, dear - I do realize that take-off is SUCH a busy time - but could you please tell the captain that the engines seem to be on fire, the wing just fell off, and the ground seems to be coming up rather more quickly than seems prudent? Thank you, dear..."

authors: Bob Jarvis - Слава Україні


text:
What makes fast decompression so dangerous for the fuselage?
There have been flight accidents which involved structural failure after fast decompression of the cabin, like
BOAC Flight 781.
I'm  thinking about how decompression can destabilize or destroy the structure of a fuselage;
I would think that a hole pinched into the cabin wall of 1 cm diameter will just cause slow decompression over minutes.
I got the impression that creating a larger hole, like removing a door, can potentially cause severe failure of the fuselage in other places than the hole.
If that is the case: what makes a hole large enough to be dangerous?
And what is the mechanism making a large hole dangerous?
Or is it that the structural failure comes first, and decompression is just a salient symptom of it?

In the case of the Comets, the decompression was a result of the failure.  Many aircraft have lost doors and survived.  The problem normally stems from the door contacting something on the way out, e.g. hitting the tail surfaces.  I don't recall ever hearing about decompression itself leading to the loss of an aircraft.  The Hollywood myth of someone shooting a hole in the fuselage causing an immediate explosion is just that - a myth!

I thought in the cases of the Comets it was a small failure in the structure, causing decompression, which causes widespread structural damage in turn.

No, but the failure started with a small crack. Decompression and further damage went in parallel, and once decompression was complete, the load which tore the fuselage apart was gone. However, by this time, you had parts of the fuselage sticking out into the free stream, and this tore it apart completely. So dynamic pressure finished the job, not internal pressure. That just got it started.

Often it's the structural failure that results in decompression.
The comet (the aircraft in your example) was vulnerable to fatigue cracking that would propagate throughout the fuselage and compromise the structural integrity. Nowadays the fuselage is designed to stop such cracks from reaching further than the next spar and planes are retired when the number of cycles has reached the design limit.
There are factors to take into account when the vessel decompresses. If portions of the vessel are closed off from each other, then the pressure difference between those sections can exceed the tolerance of the divider and cause damage. This caused the floor to collapse when the cargo door blew off in Turkish Airlines Flight 981.

The Comets also had square windows which led to pressure hotspots in the corners which in turn led to the fatigue cracks.